1. Field of the Invention
The present invention relates to an optical 2-fiber ring network for wave-division multiplex systems with several add-drop-multiplexer-terminals.
2. Description of the Prior Art
Optical networks are frequently conceived as ring networks in order to have an alternate path available when malfunctions of the regular transmission path occur. The article Multiwavelength Survivable Ring Network Architectures, A. F. Elrefaie, Bellcore, Red Bank, N.J. 07701, USA, 0-7803-0950-2/93/$3.001993IEEE, pages 1245 through 1251 discloses such ring architectures for a wavelength-division multiplex system.
The ring networks are frequently provided with what is referred to as add-drop multiplexers that serve the purpose of branching and inserting transmission channels. Previously, these functions were performed by electrical signals. In the future, optically working switching matrixes, however, are supposed to take over these functions. These optically working switching matrixes are inserted into ring structures, are realized with small outlay and exhibit protection circuits (alternate circuits).